Rozprawy doktorskie na temat „Silicon photovoltaic module”

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-145).
To meet climate targets by 2030, manufacturing capacity for photovoltaic (PV) modules must be scaled at 22-25% annual growth rate while maintaining high performance and low selling price. The most suitable material substrate to enable this scale-up is cast multicrystalline silicon (mc-Si) due to its low operating cost and capital requirements compared to other technologies. However, a new form of light-induced degradation was discovered when transitioning mc-Si to the latest high efficiency device architecture. Light- and elevated temperature-induced degradation (LeTID) causes performance to decrease by about 10% (relative) under field-relevant conditions within only four months. In this work, the root cause of LeTID is investigated in three parts: (1) Candidate hypotheses are developed for LeTID; (2) Targeted experiments are carried out toward developing a defect-based description of LeTID; and (3) The basis for a predictive model of LeTID is proposed. Techniques including minority carrier lifetime spectroscopy, synchrotron-based X-ray fluorescence, intentional contamination, and process simulation are employed to probe the defect causing LeTID. The results indicate that LeTID is caused by at least two reactants-hydrogen and one or more reactants that can be modified by high-temperature processing-and that the defect at the point of maximum degradation has recombination characteristics similar to a deep-level donor in silicon. By providing the basis for a predictive model, this work enables both identification of the root cause of LeTID and de-risking of novel solar cell architectures based on mc-Si, allowing assessment of the impact of LeTID on the future of the PV industry. This work also enables development of mitigating strategies for LeTID.
Funding from the National Science Foundation Graduate Research Fellowship Program and grants from the National Science Foundation and the U.S. Department of Energy
by Mallory Ann Jensen.
Ph. D.

This thesis presents the development of innovative tools to investigate spatially distributed properties of thin film photovoltaic devices. They are required to gain a better understanding of device behaviour driven by how such properties affect the performance of commercial-scale devices. The tools developed for this are a distributed 3D model (D3DM) as simulation software and a laser beam induced current (LBIC) system as a platform for characterisation. The D3DM was developed utilising standard circuit analysis software. It is constructed to simulate realistic device structures and current flows in thin film PV devices. Diode parameters are truly distributed and can be varied independently. The model includes a voltage dependent photocurrent which is a key characteristic of amorphous silicon based solar cells. The D3DM has been used for the investigation of spatial variation in performance due to the distributed nature and non-uniformity of diode parameters and solar cell properties. It is shown that distributed series resistance contributed from the contact layers has a significant impact on solar cell performance and efficiency. The LBIC system is an optical scanning based characterisation tool. Unlike most existing systems, this has been developed specifically for large area, module-size thin film applications. The system provides a detailed photocurrent map which reveals spatial non-uniformity and allows investigation of localised performance variation of the investigated PV devices. System development, components and their characterisation as well as different measurement techniques are described. The model is also applied to LBIC measurements where it is used for a sensitivity analysis of measurement signal with respect to certain cell parameters in cells and modules under different measurement conditions. A new limiting illuminated LBIC (li-LBIC) measurement technique was developed. It is a measurement where the laser-probed cell is brought into limiting condition by means of shading. The signal thus generated is a linear response which was previously unobtainable by typical LBIC measurements. It is unaffected by non-uniform illumination allowing the real properties of investigated cells in a monolithic series connected module to be measured non-destructively.

When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.
 

In this work are discussed photovoltaic cells. There are also discussed basic concepts of radiation source for solar cells. Also mentioned the issue of semiconductors and even the history and evolution of the solar cells. A large part deals with possibilities of photovoltaic cells degradation. In one chapter is an attempt to bring some types of photovoltaic cells and a description of the production of these modules.The practical part deals with photovoltaic modules degradation and its evaluation. Following part compares measured values with the values provided by producer of photovoltaic modules.

The durability and lifetime of photovoltaic (PV) modules is one of the chief concerns for an industry which is rapidly approaching maturity. Guaranteeing the economic viability of potential PV installations is paramount to fostering growth of the industry. Whilst certification standards have helped to improve the reliability of modules, with a significant reduction in early failures, long-term performance degradation and overall lifetimes are yet to be addressed in a meaningful way. For this, it is necessary to quantify the effects of use-environment and module design. Long-term degradation of the solder bonds in PV modules causes steady power loss and leads to the generation of more devastating, secondary mechanisms such as hot-spots. Whilst solder bond degradation is well-recognised and even tested for in certification protocols, the potential rate of degradation is not well understood, particularly with respect to different environmental conditions and material selection. The complex nature of a standard silicon PV module construction makes it difficult to observe the stresses experienced by the various components during normal operation. This thesis presents the development of a finite-element model which is used to observe the stresses and strains experienced by module components during normal operating conditions and quantifies the degradation of solder bonds under different environmental conditions. First, module operating temperatures are examined across a range of climates and locations to evaluate the thermal profiles experienced by modules. Using finite-element techniques, the thermomechanical behaviour of modules is then simulated using the same thermal profiles and a quantification of solder bond degradation potential in each location is achieved. It is shown that hot climates are responsible for the highest degradation potential, but further to this, hot environments with many ii clear sky days, allowing for large swings in module temperature, are significantly more damaging. A comparison is drawn between indoor accelerated stress procedures and outdoor exposure, such that an equivalence between test duration and location-dependent outdoor exposure can be determined. It is shown that for the most damaging climate studied, 86 standard thermal cycles is appropriate for one-year of outdoor exposure whereas the least damaging environment would require 11 standard thermal cycles. However, these conclusions may only be applicable to the specific module design which was modelled as the material selection and interaction within a device plays a major role in the thermomechanical behaviour and degradation potential. In addition to a study on the influence of use-environment, a study on the influence of the encapsulating material is conducted with a particular focus on the effects of the viscoelastic properties of the materials. It is shown that the degradation of solder bonds can vary depending on the encapsulating material. Furthermore, the intended use-environment could inform the selection of the encapsulating material. The temperature-dependency of the material properties means that some materials will mitigate thermomechanical degradation mechanisms more than others under certain conditions i.e. hotter or colder climates.

In Canada, many remote communities rely on diesel power for the majority of their energy needs, which can cause negative ecological and health impacts while limiting economic development. Bifacial photovoltaics present an alternative to diesel power. With high average latitudes, these communities show potential for large bifacial gains due to high albedo caused by snow and a high fraction of diffuse light; however, high-latitude conditions deviate from standard test conditions, with low average temperatures, light incident from many directions, and high average air masses, resulting in increased energy yield prediction uncertainty. This thesis describes the performance of bifacial silicon heterojunction cells and modules under high-latitude operating conditions, including high angles of incidence and high air masses. Optical losses in the cell and module are described, and module characteristics are incorporated in DUET, the SUNLAB's energy yield prediction software, as an incidence angle modifier and air mass modifier. The percentage change in energy yield when considering air mass is shown to increase with increasing latitude: for a single-axis-tracked installation, the annual difference in energy yield is 0.5% in a low-latitude location (33°N), and more than 2.5% in a high-latitude location (69°N). Air mass correction is demonstrated to improve energy yield prediction accuracy compared to the absence of spectral correction. This work improves energy yield prediction accuracy for high-latitude locations, facilitating adoption of solar energy in diesel-dependent remote communities in Canada and abroad.

A validated predictive model of a-Si:H solar cell arrays was developed. The performance of a-Si:H solar cells was modeled by predicting the performance before degradation first, and then modifying it with terms that account for degradation and recovery effects. A unique approach for the determination of the fundamental rate controlling parameters for the degradation and recovery process was carried out by observing the variation of the short-circuit current. The experimental annealing of a-Si:H silicon samples showed that the percent recovery from the degraded state to the as-grown state by annealing was virtually independent of the initial state at the start of the annealing process. This allowed the recovery parameters to be determined independently of the prior degradation process. An extremely simple and fast running algorithm for the long-term performance was developed in terms of the incident solar radiation, the panel temperature, and the total radiation exposed. Also it was found that the entire process of the Staebler-Wronski effect could be adequately represented by a correlation in which the degradation and recovery processes are solely a function of the total radiation exposure of the panel at ambient conditions.

Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years.

Nowadays the photovoltaic research is focused on increasing the performances, the durability and reducing the cost of production of solar cells, such as PV modules. These are the paromount fields to make photovoltaics more attractive for the energetic market. In this dissertation two of these aspects are investigated: the durability and the cost reduction issues. The fracture mechanics of the Silicon, the standard material used for the solar cells, is the main subject of the presented study. In the recent and next years the relevance of the durability studies is expected to increase more and more because of the developing of a new segment of PV, the building integrated Photovoltaic (BIPV). These new products incorporating PV modules in the building materials are curtains, walls, windows, sloped roofs, flat roofs, facades, shading systems and roofing shingles. In the new generation of BIPV systems, PV modules replace parts of the building structure, providing functional considerations and lowering costs. In this market the thin-film PV is the most promising technology because of its superior flexibility, minimal weight, and the ability to perform in variable lighting conditions. The issues of this particular PV market are not only the energy production but also the structural safety and performance in addition to architectural specifics as the shadowing. In this framework the durability, the degradation and new technology to achieve a cost reduction are of fundamental importance. In this thesis, experimental diagnostic techniques and interpretative models based on linear and nonlinear fracture mechanics for studying the phenomena of fracture in Silicon are presented. In particular the development and the use of techniques for the quantitative analysis of electroluminescence signals, for the detection of cracks in Silicon caused by thermo-elastic stresses, have been developed. The experimental results have been obtained during an extensive experimental campaign conducted at Politecnico di Torino. For the interpretation of the experimental evidence it has been proposed an original onedimensional electrical model for predicting the eect of cracks on the distribution of electric current. Subsequently, the electric field has been coupled to the mechanical, introducing an electric resistance located at the level of the crack and dependent on the crack itself. In parallel, a numerical analysis has been carried out, using the finite element codes FRANC2D and FEAP, on the phenomenon of peeling in mono-crystalline Silicon induced by thermoelastic stresses. This study, which can be very important in applications because it may allow the production of ultra-thin solar cells with a significant saving of material, is carried out in collaboration with the Institute for Solar Energy Research (ISFH), Hamelin, Germany. This process exploits the thermo-mechanical stresses due to the contrast between the elastic proviii perties of Silicon and Aluminium in line with earlier studies of the school of Harvard. It has been proposed a broad campaign experimental and numerical in order to optimize the process.

Dans le cas des installations photovoltaïques, l’onduleur est le premier élément défaillant dont il est difficile d’anticiper la panne, et peu d’études ont été faites sur la fiabilité de ce type de convertisseur. L'objectif de cette thèse est de proposer des outils et méthodes en vue d'étudier le vieillissement des modules de puissance dans ce type d'application en se focalisant sur les phénomènes de dégradation liés à des aspects thermomécaniques. En règle générale, le vieillissement accéléré des modules de puissance est effectué dans des conditions aggravées de courant (Cyclage Actif) ou de température (Cyclage Passif) pour accélérer les processus de vieillissement. Malheureusement, en appliquant ce type de vieillissement accéléré, des mécanismes de défaillances qui ne se produisent pas dans la vraie application peuvent être observés et, inversement, d'autres mécanismes qui se produisent habituellement peuvent ne pas apparaître. La première partie de la thèse se focalise donc sur la mise en place d'une méthode de vieillissement accéléré des composants semi-conducteurs des onduleurs photovoltaïques. Cela est fait en s’appuyant sur l’analyse des profils de mission du courant efficace de sortie des onduleurs et de la température ambiante, extraits des centrales photovoltaïques situées au sud de la France sur plusieurs années. Ces profils sont utilisés pour étudier les dynamiques du courant photovoltaïque, et sont introduites dans des modèles numériques pour estimer les pertes et les variations de la température de jonction des semi-conducteurs utilisés dans les onduleurs, en utilisant l’algorithme de comptage de cycles "Rainflow". Cette méthode est ensuite mise en œuvre dans deux bancs expérimentaux. Dans le premier, les composants sous test sont des modules IGBT. Les composants sont mis en œuvre dans un banc de cyclage utilisant la méthode d'opposition et mettant en œuvre le profil de vieillissement défini précédemment. Un dispositif in-situ de suivi d'indicateurs de vieillissement (impédance thermique et résistance dynamique) est également proposé et évalué. Le deuxième banc est consacré à l'étude de modules de puissance à base de MOSFET SiC. Le vieillissement est effectué dans les mêmes conditions que pour les modules IGBT et de nombreux indicateurs électriques sont monitorés mais, cette fois ci, en extrayant les composants de l'onduleur de cyclage. Les résultats obtenus ont permis de déterminer des indicateurs de vieillissement d’IGBT et de MOSFET SiC utilisés dans un onduleur photovoltaïque
In the case of photovoltaic installations, the DC/AC inverter has the highest failure rate, and the anticipation of its breakdowns is still difficult, while few studies have been done on the reliability of this type of inverter. The aim of this PhD is to propose tools and methods to study the ageing of power modules in this type of application, by focusing on ageing phenomena related to thermo-mechanical aspects. As a general rule, the accelerated ageing of power modules is carried out under aggravated conditions of current (Active Cycling) or temperature (Passive Cycling) in order to accelerate the ageing process. Unfortunately, when applying this type of accelerated ageing tests, some failure mechanisms that do not occur in the real application could be observed, while inversely, other mechanisms that usually occur could not be recreated. The first part of the PhD focuses on the implementation of an accelerated ageing method of the semiconductor devices inside photovoltaic inverters. This is accomplished by analyzing the mission profiles of the inverter’s output current and ambient temperature, extracted over several years from photovoltaic power plants located in the south of France. These profiles are used to study photovoltaic current dynamics, and are introduced into numerical models to estimate losses and junction temperature variations of semiconductors used in inverters, using the cycle counting algorithm “Rainflow”. This method is then performed in two experimental test benches. In the first one, the devices under test are IGBT modules, where the accelerated ageing profile designed is implemented using the opposition method. Moreover, an in-situ setup for monitoring ageing indicators (thermal impedance and dynamic resistance) is also proposed and evaluated. The second bench is devoted to study the ageing of SiC MOSFET power modules. The accelerated ageing test is carried out under the same conditions as for the IGBT modules with more monitored electrical indicators, but this time by disconnecting the semiconductor devices from the inverter. The results obtained allowed to determine several potential ageing indicators of IGBTs and SiC MOSFETs used in a photovoltaic inverter

Les cellules et modules photovoltaïques s’échauffent considérablement en conditions réelles de fonctionnement, ce qui est néfaste pour leur rendement de conversion et leur durée de vie. Pourtant, les aspects thermiques sont encore peu considérés, voire complètement ignorés lors de la conception des dispositifs photovoltaïques. Dans ce contexte, l'objectif de cette thèse est d'étudier une stratégie novatrice pour limiter l'échauffement : le refroidissement par échange radiatif avec le ciel. Cette approche consiste à optimiser l'échange radiatif dans les gammes spectrales où il n'y a pas de conversion photovoltaïque, notamment dans le moyen infrarouge pour profiter de la fenêtre de transparence qu'offre l’atmosphère dans la gamme 8-13 µm. Bien que prometteuse, de nombreux verrous restent à lever pour saisir les tenants et les aboutissants de cette stratégie, aussi bien du point de vue théorique que du point de vue expérimental. Grâce à un modèle électrique et thermique spécialement développé à cet effet, le bénéfice théorique que le refroidissement radiatif avec le ciel peut apporter aux dispositifs photovoltaïques est d'abord quantifié. Le profil d'émissivité idéal est également déterminé. Plus généralement, des lignes directrices et des ordres de grandeurs sont établis pour une vaste gamme de dispositifs basés sur une technologie monojonction. Les pistes expérimentales pour atteindre le profil d'émissivité idéal sont ensuite mises en lumière. A l'échelle d'un module en silicium cristallin, il apparaît que la voie la plus prometteuse concerne l'ingénierie de l'interface air-verre. A cet égard, une structure optique basée sur une multicouche diélectrique est proposée et analysée. Pour guider d'éventuelles études futures, un ensemble d'outils numériques et méthodologiques pour trouver, concevoir, et quantifier le bénéfice des structures optiques est présenté. En complément de ces résultats spécifiques au refroidissement radiatif avec le ciel, un modèle opto-électro-thermique de cellules en silicium est développé. Ce dernier a pour but de prédire les performances en conditions réelles de fonctionnement directement à partir de la connaissance des matériaux et de l'architecture de la cellule. Nous montrons notamment comment ce modèle d'un nouveau genre permet d'ouvrir de nouvelles voies pour continuer à augmenter la production d'électricité photovoltaïque via une ingénierie plus consciente des effets thermiques
Photovoltaic solar cells and modules heat up considerably under real operating conditions, which is detrimental to their conversion efficiency and their lifetime. However, thermal aspects are still little taken into account, or even completely ignored, in the design of photovoltaic devices. In this context, the objective of this work is to study an innovative strategy to limit overheating: radiative sky cooling. This approach consists of optimising radiative heat exchange in spectral ranges where there is no photovoltaic conversion, in particular in the mid-infrared range to take advantage of the atmospheric transparency window between 8-13 µm. Although promising, many theoretical and experimental obstacles have to be adressed in order to fully grasp the opportunities and challenges of radiative sky cooling for photovoltaics. Using an in-house developped electrical and thermal model, the theoretical benefit that radiative sky cooling can bring to photovoltaic devices has been quantified. The ideal emissivity profile was also determined. More generally, guidelines and orders of magnitude were established for a wide range of devices. The experimental pathways for achieving the ideal emissivity profile have been unveiled. For crystalline silicon module, it appears that the most promising approaches relate to the engineering of the air-glass interface. In this respect, an optical structure based on a dielectric multilayer is proposed and analysed. To guide future studies, a set of numerical and methodological tools that enable to identify, design, and quantify the benefit of optical structures has been developed. In addition to these specific results for radiative sky cooling, an opto-electro-thermal model of silicon cells is presented. This model aims at predicting the performance under real operating conditions directly from the materials and the architecture of the cell. In particular, we show how this model paves the way to further increase photovoltaic electricity production through more thermally aware engineering

L’interface entre le silicium amorphe (a-Si:H) et le silicium cristallin (c-Si) est un constituent clés de cellules solaires à haut rendement reposant sur des procédés à basse température. Trois propriétés de l’interface déterminent le rendement des cellules solaires à hétérojonction de silicium: les décalages de bandes entre a-Si:H et c-Si, les défauts d’interface et la courbure de bande dans c-Si. Ces trois aspects sont traités dans ces travaux de thèse.Dans un premier un temps, un calcul analytique de la courbure de bande dans c-Si est développé. Il repose sur l’approximation d’une densité d’état (DE) constante dans la bande interdite de a-Si:H. L’influence des principaux paramètres de la structure sur la courbure de bande est étudiée : décalage de bande, densité d’état dans a-Si:H, défaut d’interface, etc. La présence d’un effet de confinement quantique est discutée. Grâce à une comparaison entre ces calculs et des mesures de conductance planaire en fonction de la température sur des structures (p)a-Si:H/(n)c-Si et (n)a-Si:H/(p)c-Si, les décalages de bande de valence et de conduction ont pu être estimés à 0.36 eV et 0.15 eV respectivement. En outre, il est montré que le décalage de la bande de valence est indépendant de la température, alors que le décalage de la bande de conduction suit les évolutions des bandes interdites de c-Si et a-Si:H. Ces mesures tendent à prouver que le ‘branch point’ dans a-Si:H est indépendant du dopage.Ensuite, les calculs analytiques sont approfondis pour prendre en compte différents aspects de la structure complète incorporée dans les cellules : contact avec un oxyde transparent conducteur, présence d’une couche de a-Si:H non-dopée à l’interface. A l’aide de simulations numériques et à la lumière de mesures de conductance planaire conjuguées à des mesures de la qualité de passivation de l’interface, des pistes pour optimiser les cellules à hétérojonction sont commentées. En particulier, il est montré qu’un optimum doit être trouvé entre une bonne passivation et une courbure de bande suffisante. Ceci peut être accompli par un réglage fin des propriétés de la couche tampon (épaisseur, dopage), du contact (travail de sortie élevé) et de l’émetteur (p)a-Si:H (densité de défauts et épaisseur). En particulier, un émetteur avec une DE importante conduit paradoxalement à de meilleures performances.Enfin, un nouveau type d’interface a été développé. La surface de c-Si a été oxydée volontairement dans de l’eau pure dé-ionisée à 80 °C avant le dépôt de (p)a-Si:H afin d’obtenir une structure (p)a-Si:H/SiO2/(n)c-Si. A l’aide d’un modèle de courant par effet tunnel implémenté dans le logiciel de simulation numérique AFORS-HET, l’effet d’une couche à grande bande interdite (comme c’est le cas pour SiO2) sur les performances de cellules est étudié : le facteur de forme et le courant de court-circuit sont extrêmement réduits. En revanche, une couche de SiO2 n’a que peu d’impact sur les propriétés optiques de la structure. Expérimentalement, les échantillons réalisés montrent une qualité de passivation à mi-chemin entre le cas sans couche tampon et le cas avec (i)a-Si:H : ceci est expliqué par la présence d’une charge fixe négative dans l’oxyde. La courbure de bande dans c-Si est moins affectée par la présence d’une couche d’oxyde que d’une couche de (i)a-Si:H. Les cellules solaires réalisées démontrent que le concept a le potentiel d’aboutir à de hauts rendements : sur des structures non-optimisées, une tension de court-circuit supérieure à 650 mV a été démontrée, alors que l’oxyde ne semble pas limiter le transport de charge
The interface between amorphous silicon (a-Si:H) and crystalline silicon (c-Si) is the building block of high efficiency solar cells based on low temperature fabrication processes. Three properties of the interface determine the performance of silicon heterojunction solar cells: band offsets between a-Si:H and c-Si, interface defects and band bending in c-Si. These three points are addressed in this thesis.First, an analytical model for the calculation of the band bending in c-Si is developed. It assumes a constant density of states (DOS) in the a-Si:H band gap. The influence of most parameters of the structure on the band bending is studied: band offsets, DOS in a-Si:H, interface defects, etc. The presence of quantum confinement at the interface is discussed. Analytical calculations and temperature dependent planar conductance measurements are compared such that the band offsets on both (p)a-Si:H/(n)c-Si and (n)a-Si:H/(p)c-Si can be estimated: the valence band offset amounts 0.36 eV while the conduction band offset is 0.15 eV. In addition, it is shown that the valence band offset is independent of temperature whereas the conduction band offset follows the evolutions of c-Si and a-Si:H band gaps with temperature. A discussion of these results in the frame of the branch point theory for band line-up leads to the conclusion that the branch point in a-Si:H is independent of the doping.Then, analytical calculations are developed further to take into account the real solar cell structure where the a-Si:H/c-Si structure is in contact with a transparent conductive oxide and an undoped buffer layer is present at the interface. Measurements of the planar conductance and of the interface passivation quality are interpreted in the light of analytical calculations and numerical simulations to open a way towards a method for the optimization of silicon heterojunction solar cells. It is particularly shown that a trade-off has to be found between a good passivation quality and a significant band bending. This can be realized by tuning the buffer layer properties (thickness, doping), the TCO-contact (high work function) and the emitter (defect density and thickness). Interestingly, an emitter with a high DOS leads to better cell performances.Finally, a new type of interface has been developed, that was not applied to heterojunction solar cells so far. The c-Si surface has been oxidized in deionized water at 80 °C before the (p)a-Si:H emitter deposition such that (p)a-Si:H/SiO2/(n)c-Si structures were obtained. A tunneling current model has been developed, implemented in the 1D numerical device simulator AFORS-HET and used to study the effect of a wide band gap interfacial layer (as it is the case for SiO2) on cell performance: the fill-factor and the short-circuit current are dramatically reduced for thick and high barriers. However, a SiO2 layer has only little impact on optical properties. Fabricated samples show a passivation quality halfway between samples with no buffer layer and with an (i)a-Si:H buffer layer: this is explained by the presence of a negative fixed charge in the oxide. The band bending in (n)c-Si is higher with an oxide layer than with an (i)a-Si:H buffer layer. Solar cells demonstrate that this new concept has the potential to achieve high power conversion efficiencies: for non-optimized structures, an open-circuit voltage higher than 650 mV has been demonstrated, while the oxide does not seem to create a barrier to charge transport

Classiquement, la chaîne de conversion de l’énergie électrique des centrales photovoltaïques comporte un champ photovoltaïque (PV) délivrant une tension maximale de 1kV suivi d’un hacheur élévateur connecté à un onduleur de tension triphasé. Cette chaîne de conversion à deux étages (DC/DC + DC/AC) est ensuite raccordée sur le réseau moyenne tension au travers d’un transformateur BT/HTA. Dans l’objectif de simplifier les systèmes de conversion PV, ce travail de recherche s’intéresse à l’étude et la mise en œuvre d’une topologie DC/AC n’employant qu’un seul étage de conversion : l’Onduleur de Courant triphasé. Bien que relativement simple, l’Onduleur de Courant présente comme inconvénient majeur les pertes par conduction. Pour pallier ce problème, des interrupteurs à grand-gap au Carbure de Silicium (SiC) sont employés, ce qui permet de convertir de l’énergie de façon performante (η>98.5%) tout en gardant une fréquence de commutation élevée (plusieurs dizaines de kHz). Les modules à semi-conducteurs de puissance du marché n’étant pas compatibles avec ce type de convertisseur, des modules particuliers en SiC ont été développés dans le cadre de la thèse. La caractérisation dynamique de ces nouveaux modules est réalisée dans le but de servir de base à la conception d’un démonstrateur de l’Onduleur de Courant d’une puissance nominale de 60kW. Enfin, le rendement de la partie semi-conducteur de puissance est évalué par une méthode calorimétrique confirmant l’aptitude de la topologie à fonctionner à des fréquences de commutation supérieures. L’originalité de ces travaux réside principalement dans la conception, caractérisation et mise en œuvre de ce nouveau module de puissance adapté à cette topologie connue, mais peu étudiée à l’heure actuelle avec des interrupteurs au SiC
Classically, the energy conversion architecture found in photovoltaic (PV) power plants comprises a multitude of solar arrays delivering a maximum voltage of 1kV followed by a step-up chopper connected to a three-phase voltage source inverter. This two-stage conversion system (DC/DC + DC/AC) is then connected to the MV grid through a LV/MV transformer. In order to simplify the PV systems, this research work focuses on the study and implementation of a DC/AC topology employing a single conversion stage: the three-phase current source inverter (CSI). Although relatively simple, the CSI presents as major drawback the conduction losses. To deal with this problem, wide-bandgap silicon carbide (SiC) semiconductors are used, which allows to efficiently convert energy (η> 98.5%) while keeping a relatively high switching frequency (several tens of kHz). Nonetheless, since the available power semiconductor modules on the market are not compatible with the CSI, a novel 1.7kV SiC-based module is developed in the context of the thesis. Thus, the dynamic characterization of the new SiC device is carried out and serves as a basis for the design of a 60kW Current Source Inverter prototype. Finally, the inverter’s semiconductor efficiency is evaluated through a calorimetric method, confirming the ability of the topology to operate at higher switching frequencies. At the present time, little research has been conducted on the CSI implementation with SiC devices. The originality of this work lies mainly in the design, characterization and implementation of the new SiC power module adapted to this well-known inverter topology

The solar industry is one of the fastest-growing energy industries in the global market. The reason is a combination of the falling prices of modules and inverters and increased conversion to fossil-free energy production. When a photovoltaic module reaches the end of its life it needs to be replaced and discarded, which can create a sustainability problem depending on how this is managed. Today, less than 10% of the global photovoltaic waste is recycled. Only the European Union has implemented photovoltaic waste regulations in the form of the WEEE Directive, which requires that 85% of the waste is collected and at least 80% of waste collected must be prepared for reuse or recycling. This master thesis examines the energy technical, economic, and political conditions for a Swedish photovoltaic recycling plant. This is done through a literary study that is enhanced with calculations of future potential waste volumes and their economic value. As an alternative to a Swedish plant, the energy consumption for transporting waste to existing recycling plants in Europe is evaluated. The photovoltaic technologies included in this work are silicon-based mono-and polycrystalline modules, cadmium tellurium (CdTe) and copper indium gallium selenide (CIGS). Based on the calculations and the literature study, the energy technical conditions are good and not a barrier for a potential facility, the political conditions are deficient, and regulations need further development. The economic conditions constitute the largest barrier as waste volumes are not large enough for a Swedish facility to be economically profitable until 2042. The energy consumption for transport to existing recycling plants in Europe was 22 MJ/module for silicon-based mono-and polycrystalline modules and 10 MJ/module for CdTe modules. Which is a good alternative to a Swedish plant as collection processes and recycling processes are already in place.

The aim of this work is informed first about photovoltaics universally, works to inform the photovoltaic panels and complete plants. The work also includes instructions on how to implement PVP in accordance with law. Another part is the rough draft of the photovoltaic power 30 kWp, which can be placed on the house, computation and calculation of investment and them profitable investments to time. Design is made in two separate forms of the Fronius Solar and Sunny Design, their outputs are compared. The practical part of this work cooperates with the company SOLARTEC Ltd. for experimental measurements of the photovoltaic system and develop a methodology for setting the properties of real solar systems in operation from the measured data then stored in a database. These data further evaluate and compare the similar operating conditions. This data will show as the course of production of electricity during the typical day in percentage terms, depending on the incident irradiance, cell temperature, angle of incident radiation, etc. We can compare what it looks like an ideal day in terms of production of photovoltaic power, with the other days. Further are in work mentioned histograms achievement panel behind classical day and behind all - time investigation.

Until a few decades ago few people could imagine that the photovoltaic, solar thermal and other power based on renewable resources, will become a reality. Today people from all over the world on the contrary try at full blast derive benefit from of all possible available source. Using sunlight as a source of energy is first enforced only for small devices such as calculators for charging the battery, but now we are able to produced energy from the sun to supply people around the world. Of course it is not possible supply consumer sector plus firm only from performances renewable power supply. Therefore endeavour is derive benefit from classical energy production at the same time with others power supply. The basic components of photovoltaic and solar thermal power are panels. The panels are made of different materials in different shapes and sizes. During production, the resulting effect looks in addition to costs associated with production. For photovoltaic and solar thermal power plant requires sufficient sunlight. The sunshine has biggest intensity on south of ours planets. Therefore endeavour is build lump these power station just in stand with bigger intensity sunshine. One of them is just Cyprus, too.

碩士
正修科技大學
電機工程研究所
101
Green energy is developing in Taiwan as result of the shortage of energy on the world, raising price of crude oil and global warming climate. Efficiency using solar energy is a common dream for scientists. Therefore, the first generation, the second generation and the third generation photovoltaic (PV) cell are developed rapidly. This thesis focuses on CIGS solar cell efficiency. In the same condition like as irradiation, elevation and environment temperature to evaluate the efficiency difference of CIGS and poly crystal silicon PV module. The numerical data of CIGS is recorded by monitoring software to analysis and to compare with poly crystal silicon PV module.

碩士
國立成功大學
機械工程學系碩博士班
101
In the light of former studies, the elevation of the PV temperature declines solar to electrical energy conversion efficiency by 0.4 - 0.5 (%．K-1) for crystal silicon PV when it rises above the characteristic power conversion temperature of 25℃. Therefore, this research decreases the operating temperature of module to improve its performance by changing materials of ethylene vinyl acetate and adding the cooling fins. Numerical and experimental methods are used to get the temperature of central base sheet and each layer, output power, current, voltage, conversion efficiency, relative power, the effect of fin’s radiation and the influence of force convection under (1) low irradiance; (2) nominal operating cell temperature (NOCT); (3) standard test condition (STC) and (4) the solar module with cooling fins. In the research, the main control factors are the material of rear EVA, the conductivity of module of back sheet, the emissivity and the numbers of fin. The results show that the module’s temperature and output power increases when the irradiance elevates, but the conversion efficiency of module decreases oppositely. The change of EVA can increase the incident light of cell. With the high conductivity of back sheet, the concentrative heat of cell originally can be spread into the frame. Better results are found with four straight fins in this research, and the high emissivity of fin can elevate radiative heat of fin. Therefore, the above improvements can elevate the relative power and performance of the module. Finally, in order to understand the effect of forced convection and radiation, the performance of the best module with high emissivity cooling fins and the modules with different emissivity cooling fins blown by fan are compared in this study. The results show that the effect of radiation can be almost ignored if the forced convection is taken into consideration.

碩士
國立成功大學
機械工程學系碩博士班
100
According to former studies, the elevation of the PV temperature reduces solar to electrical energy conversion efficiency by 0.4 - 0.5 (%．K-1) for crystal silicon PV when it rises above the characteristic power conversion temperature of 25℃. Therefore, the performance of module is improved by changing materials of ethylene vinyl acetate and back sheet to decrease the operating temperature of module in this study. Under (1) low irradiance; (2) nominal operating cell temperature (NOCT) and (3) standard test condition (STC), numerical and experimental methods are used to get (1) the central back sheet’s temperature and each layer’s temperature; (2) output power, current and voltage; (3) conversion efficiency and relative power; (4) the effect of back sheet’s radiation; (5) the percentage of each thermal mechanism; (6) contributions of factors. Then, the above results will be verified through the full-scale experiments. Findings from this research will be applied in industry. In the research, the main control factors are the material of rear EVA and the back sheet’s conductivity and emissivity. The results show that the module’s temperature and output power increase when the irradiance elevates, but the conversion efficiency of module decreases. The high emissivity of module’s back sheet can double dissipate the radiative heat from the back sheet. The concentrative heat of cell can be spread into the frame by the high conductivity of back sheet. The white rear EVA can increase the amount of incident light into cell. Therefore, these three mechanisms can improve operating temperature and the amount of incident light into cell and then elevate the relative power and performance of the module. Finally, although the gain value of module’s performance has a gap between the steady-state in-lab experiment and the transient full-scale experiment, their trends are the same. Consequently, if the intersections among factors can be improved, the compound effect can tend toward the linear superposition of each factor and then the maximum relative power can be achieved.

碩士
國立中央大學
國際永續發展碩士在職專班
106
The goal of this thesis is to assess the economic feasibility of a recycling facility for crystalline silicon based PV modules. Two cases are described in this study, the first one is the building up and operating a recycling facility located in the north region of Italy and the second one is located in the north region of Honduras. This thesis utilizes an economic model called the discounted cash flows in order to assess the economic feasibility of the recycling facilities. A sensitivity analysis was applied in order to identify the range of parameters values within which a project can remain economical viable. The sensitivity analysis was applied to the critical values that affect the viability of the project (Investment, collection, process and conferred cost, as well to the prices of the material chosen to be recycled). The discounted cash flow method results shows for the first case the unprofitability of the recycling plant located in Italy in the entire scenarios including the sensitivity analysis. In the other hand the results from the economic method for the second case, described the profitability of the recycling plant located in Honduras, revenues are obtained in the fourth year of operation. The results of the sensitivity analysis for the second case confirm the feasibility of the project obtaining revenues from the facility in the third year as the best scenario

碩士
國立中央大學
光電科學與工程學系
101
As the decreasing of energies such as fossil fuel, the energy price is getting higher herewith serious issues of pollution, the greenhouse effect, and climatic anomalies. On March, 2011, the Fukushima Daiichi nuclear disaster in Japan injured thousands of people to increase the safety concern of nuclear. Besides, the treatment of nuclear waste is still a big problem. Renewable energies such as solar power, wind power, and geothermal power, are good solutions to substitute those non-renewable resources. For the lack of natural resources in Taiwan, the renewable resources are more important. Solar power is the best solution since it exits everywhere. The fabrication technology of solar cells is similar with the one of semiconductors, which is mutual in Taiwan. In this research, a mono-crystalline silicon photovoltaic system and a poly-crystalline silicon photovoltaic system were build to analyze their performances and connected to commercial DC-to-AC (D/A) inverters in real environment. These D/A inverters were developed with maximum power point tracking (MPPT) function. The AC power generated from the photovoltaic systems was transferred from DC powers to the on-grid system directly. A LabView program was developed to record the generated powers and the temperatures of solar modules. The final results were calculated including the data of solar irradiance provided by the Department of Atmospheric Science of National Central University. In the analysis we can understand the relationships between photovoltaic module temperature, solar irradiance, and efficiency.

Σκοπός αυτής της διπλωματικής εργασίας είναι η θεωρητική μελέτη φωτοβολταϊκών πλαισίων χρησιμοποιούμενων σε διαστημικές εφαρμογές, περιγράφοντας την τεχνολογία και τη λειτουργία τους, καθώς και την ιστορική εξέλιξη τους τις τελευταίες δεκαετίες από το 1950 έως σήμερα. Στα πλαίσια αυτά περιγράφονται οι ηλιακές συστοιχίες για διαστημικές εφαρμογές, οι συνηθισμένοι τύποι ημιαγωγικών υλικών για τα πλαίσια, όπως το πυρίτιο Si και το αρσενιούχο γάλλιο GaAs και οι απαιτήσεις των. Αρχικά, μελετάται ποιες παράμετροι επηρεάζουν την απόδοση των φωτοβολταϊκών κυττάρων στο διάστημα και επιπλέον οι επιπτώσεις της διαστημικής ακτινοβολίας και θερμοκρασίας στην λειτουργία των πλαισίων. Στη συνέχεια παρουσιάζονται τα προηγμένα ηλιακά κύτταρα πυριτίου Si και τα υψηλής απόδοσης άμορφου πυριτίου που παρουσιάζουν βελτιωμένη ενεργειακή απόδοση του πλαισίου. Οι βέλτιστες παράμετροι των δομών για τις διαστημικές εφαρμογές, φαίνεται πλέον να επιτυγχάνονται με τα ευρέως χρησιμοποιούμενα ηλιακά κύτταρα πολυεπαφών multijunction MJ, που είναι κύτταρα ιδιαιτέρου τρόπου σχεδιασμού. Οι παράμετροι επηρεασμού της απόδοσης τους αναλύονται καθώς και οι επιπτώσεις των εξωτερικών συνθηκών. Μεγάλης σημασίας θεωρείται ο σχεδιασμός της ηλιακής συστοιχίας στο διάστημα και οι απαιτήσεις σχεδίασης για αξιόπιστη απόδοση και μεγάλη διάρκεια ζωής. Στη μελέτη αυτή αναλύουμε και τις δομές εκείνες που μπορούν να βελτιώσουν την απόδοση των διαστημικών ηλιακών κυττάρων. Οι πιο ελπιδοφόρες και πιο πολλά υποσχόμενες δομές είναι αυτές των μεταμορφικών «metamorphic» και ανεστραμμένων μεταμορφικών «inverted-metamorphic» ηλιακών κυττάρων σε σχέση με τα κλασικά "latticed matched" ηλιακά κύτταρα και αυτες οι δομές θα συνεχίσουν να βρίσκονται στο επίκεντρο για τις επόμενες δεκαετίες. Επιπλέον προϊόν της παρούσας διπλωματικής εργασίας, είναι η πειραματική μελέτη της συμπεριφοράς ενός φωτοβολταϊκού πλαισίου μονοκρυσταλλικού πυριτίου m-Si ισχύος αιχμής 80 W σε πραγματικές συνθήκες λειτουργίας στη γη, υπό την επίδραση διαφόρων εξωτερικών παραγόντων, όπως προσπίπτουσα ακτινοβολία, θερμοκρασία και γωνία κλίσης. Με στόχο την εκτίμηση της ενεργειακής απόδοσης και της ανίχνευσης της βέλτιστης τιμής αυτής πραγματοποιήθηκαν μετρήσεις με την βοήθεια του PVPM στη διάρκεια του έτους 2009 – 2010. Συγκεκριμένα περιλαμβάνονται δυο περίοδοι μετρήσεων: α) Απρίλιος 2009 έως Ιούλιος 2009, όπου πραγματοποιήθηκαν μετρήσεις ανά μια ώρα για όλες τις γωνίες κλίσης 0, 10, 20, 30, 40, 50, 60, 70, 80ο (μια ημέρα κάθε εβδομάδα) με την βοήθεια της ρυμθιζόνεμης βάσης και β) Αύγουστος 2009 έως Μάρτιος 2010, όπου πραγματοποιήθηκαν ολοήμερες μετρήσεις ανά 5 λεπτά, κάθε εβδομάδα με την βοήθεια φορητού υπολογιστή σε συγκεκριμένη κλίση 38ο, που αντιστοιχεί στο γεωγραφικό πλάτος της περιοχής της Πάτρας. Όλα αυτά οδηγούν σε μια ολοκληρωμένη εικόνα της ενεργειακής συμπεριφοράς και απόδοσης του φωτοβολταϊκού πλαισίου μας καθώς και των συνθηκών που οδηγούν σε βέλτιστες φωτοβολταϊκές ιδιότητες Η ετήσια αποδιδόμενη ενέργεια υπολογίστηκε ελαφρώς υψηλότερη από μετρήσεις γενικά αναφερόμενες από το ΚΑΠΕ. Αυτό θεωρούμε ότι οφείλεται στο γεγονός ότι η διάταξη μας δεν κατέγραφε μετρήσεις καθ όλη τη διάρκεια του έτους με αποτέλεσμα να μην είναι ακριβής η διάρκεια της ημέρας και η τιμή της προσπίπτουσας ηλιακής ακτινοβολίας. Μέσω του PVsyst προγράμματος προσπαθήσαμε να προσομοιώσουμε την ενεργειακή απόδοση του πλαισίου μονοκρυσταλλικού πυριτίου υπολογιστικά τόσο με τα πειραματικά μετεωρολογικά δεδομένα όσο και με τα μετεωρολογικά δεδομένα μέσω του προγράμματος Meteonorm και να την συγκρίνουμε με την πειραματική και επιπλέον να βρούμε την βέλτιστη απόδοση του ανάλογα με την κλίση και τον προσανατολισμό του. Η εξομοίωση με δεδομένα του προγράμματος Meteonorm 6.1 έδωσε τη διαφορά της αποδιδόμενης ενέργειας κάθε περίπτωσης, μεταξύ αυτής και της προηγούμενης μεθόδου.
The purpose of this thesis, is the theoretical study of solar modules used in space applications, together with the description of their technology and operation, and the historical development in recent decades from 1950 to today. In this context we analyzed the solar arrays for space applications, the requirements of materials for solar cells and the common types of semiconductor materials for modules, such as silicon Si and gallium arsenide GaAs. Initially, we studied what external factors affect the performance of solar cells in space and also the effects of space radiation and temperature. Further, we described the advanced silicon solar cells and the high-efficiency amorphous silicon solar cells, that improve the energy efficiency significant. For the optimal solution for space applications, we then analyzed thoroughly the most widely used in space multijunction MJ solar cells and their design, the performance parameters and the effects of external factors. To summarize the theoretical study, we studied the design of the solar array in space and the design requirements for reliable performance and longevity. Finally, there are many ways we can improve the performance of space solar cells. The most promising methods are those of metamorphic «metamorphic» and reverse metamorphic «inverted-metamorphic» solar cells compared to the classic "latticed matched" solar cells and will continue to be in the forefront for decades to come. Additional to the subject of this thesis, is the experimental study of the behavior of a photovoltaic monocrystalline silicon module m-Si 80 W peak power at real operation conditions under the influence of various external factors such as incident radiation, temperature and tilt. In order to estimate the energy efficiency we took measurements with the help of PVPM in the year 2009 - 2010. Specifically, it consists of two measurement periods: a) April 2009 to July 2009, when measurements were taken every hour for all angles 0, 10, 20, 30, 40, 50, 60, 70, 80 every week with the help of special structure and b) August 2009 to March 2010, when measurements were made all day, every five minutes, each week with a notebook in a particular inclination 38ο, corresponding to the latitude of the region of Patras. All these help us to gain a comprehensive idea of their behavior and performance of our photovoltaic modules. We also observed variation in the results in comparison with CRES databases due to the fact that we could not continuously conduct every day of the year. Using PVsyst we tried to verify our experimental results and find the best solutions for the tilt and orientation of the PV modules. With the program PVsyst we tried to simulate the performance of monocrystalline silicon solar cell using computational frameworks and to compare them with the experimental results. Finally it was also simulated with the data given from the database of the program Meteronorm 6.1 so as to compare both methods.

碩士
國立中央大學
光電科學與工程學系
103
Three different kinds of photovoltaic modules, mono-crystalline silicon, poly-crystalline silicon and CIGS solar cells were chosen conversion efficiency to measure the outdoor temperature, efficiency and light intensity in order to understand their properties and study the physical mechanism of internal differences. A CIGS thin-film solar cell module placed on a biaxial tracker was setup to compare the efficiency with a fixed module and to analyze if the generating power capacity can cover the cost of the tracker or not. In order to figure the series of questions, the three techniques of solar cell modules were installed in the roof of a building in Chungli, Taoyuan. Based on the analysis of the measured data in the real environment, the relationships of the weather conditions with the specifications, the physical mechanisms of the mono-crystalline silicon, poly- crystalline silicon and the CIGS photovoltaic modules can be achieved. Finally, we found that the highest efficiency of the mono-crystalline silicon and the CIGS photovoltaic modules is 13.29% and 8.04%, respectively. The temperature coefficients of the mono-crystalline silicon, the poly-crystalline silicon and the CIGS photovoltaic modules are βMono-Si=(0.0458°C-1) > βPoly-Si=(0.0446°C-1) > βCIGS=(0.0285°C-1). The irradiance coefficients are γPoly-Si=(0.1212) > γCIGS=(0.1034) > γMono-Si=(0.0683). And the average energy increasing ratio with the tracker is 1.32

abstract: ABSTRACT As the use of photovoltaic (PV) modules in large power plants continues to increase globally, more studies on degradation, reliability, failure modes, and mechanisms of field aged modules are needed to predict module life expectancy based on accelerated lifetime testing of PV modules. In this work, a 26+ year old PV power plant in Phoenix, Arizona has been evaluated for performance, reliability, and durability. The PV power plant, called Solar One, is owned and operated by John F. Long's homeowners association. It is a 200 kWdc, standard test conditions (STC) rated power plant comprised of 4000 PV modules or frameless laminates, in 100 panel groups (rated at 175 kWac). The power plant is made of two center-tapped bipolar arrays, the north array and the south array. Due to a limited time frame to execute this large project, this work was performed by two masters students (Jonathan Belmont and Kolapo Olakonu) and the test results are presented in two masters theses. This thesis presents the results obtained on the south array and the other thesis presents the results obtained on the north array. Each of these two arrays is made of four sub arrays, the east sub arrays (positive and negative polarities) and the west sub arrays (positive and negative polarities), making up eight sub arrays. The evaluation and analyses of the power plant included in this thesis consists of: visual inspection, electrical performance measurements, and infrared thermography. A possible presence of potential induced degradation (PID) due to potential difference between ground and strings was also investigated. Some installation practices were also studied and found to contribute to the power loss observed in this investigation. The power output measured in 2011 for all eight sub arrays at STC is approximately 76 kWdc and represents a power loss of 62% (from 200 kW to 76 kW) over 26+ years. The 2011 measured power output for the four south sub arrays at STC is 39 kWdc and represents a power loss of 61% (from 100 kW to 39 kW) over 26+ years. Encapsulation browning and non-cell interconnect ribbon breakages were determined to be the primary causes for the power loss.
Dissertation/Thesis
M.S.Tech Technology 2012

abstract: The object of this study was a 26 year old residential Photovoltaic (PV) monocrystalline silicon (c-Si) power plant, called Solar One, built by developer John F. Long in Phoenix, Arizona (a hot-dry field condition). The task for Arizona State University Photovoltaic Reliability Laboratory (ASU-PRL) graduate students was to evaluate the power plant through visual inspection, electrical performance, and infrared thermography. The purpose of this evaluation was to measure and understand the extent of degradation to the system along with the identification of the failure modes in this hot-dry climatic condition. This 4000 module bipolar system was originally installed with a 200 kW DC output of PV array (17 degree fixed tilt) and an AC output of 175 kVA. The system was shown to degrade approximately at a rate of 2.3% per year with no apparent potential induced degradation (PID) effect. The power plant is made of two arrays, the north array and the south array. Due to a limited time frame to execute this large project, this work was performed by two masters students (Jonathan Belmont and Kolapo Olakonu) and the test results are presented in two masters theses. This thesis presents the results obtained on the north array and the other thesis presents the results obtained on the south array. The resulting study showed that PV module design, array configuration, vandalism, installation methods and Arizona environmental conditions have had an effect on this system's longevity and reliability. Ultimately, encapsulation browning, higher series resistance (potentially due to solder bond fatigue) and non-cell interconnect ribbon breakages outside the modules were determined to be the primary causes for the power loss.
Dissertation/Thesis
M.S.Tech Electrical Engineering 2013

碩士
高苑科技大學
電機工程研究所
104
Abstract In our discussion of light induced degradation for normal mono/Poly modules and passivated emitter and rear cell mono/poly crystalline silicon solar photovoltaic modules, we found that two different process technology for the p-type solar module on load and unload system had different light induced degradation. When the modules were exposured to the sun over 80 KWh/m² , the power was no clear attenuation and gradually stabilized. According to the measurement of maximum power and electroluminescent fluorescent, we found that the passivated emitter and rear cell mono/poly modules of light induced degradation is more clear than the normal mono/Poly modules. It should be a relationship with boron and oxygen atom content of the passivated emitter and rear cell mono/poly modules. Sunlight will result in the boron-oxygen complexes increasing and the maximum power decreasing. Key Words: P-type mono/poly crystalline silicon solar photovoltaic modules, Passivated Emitter and Rear Cell mono/poly crystalline silicon solar photovoltaic modules, light induced degradation

Ph.D.
A one-dimensional numerical simulation of photovoltaic (PV) cells has been written, and has been designated RAUPV2. An algorithm for determining the optical generation rate profile, taking into account multiple internal reflections in a multilayer cell has been developed. A method which enables realistic boundary values to be calculated, using RAUPV2 itself, has been developed. This method allows all three boundary values (', Fn and Fp) at each surface, to be determined, without the need to specify any additional input parameters. A comprehensive set of input parameters for aSi:H PV cells has been established, in consultation with the literature. Dangling-bond theory has been described and input parameters for dangling-bond defects have been presented. The effect of surface states in the p-layer on the contact potential at the TCO/p interface has been investigated. It was found that there is an intimate relationship between the contact potential and the parameters pertaining to the surface states. A simple method has been demonstrated, which has allowed RAUPV2 to reproduce the J-V curve of an existing aSi:H PV cell. The method requires that only the dangling-bond concentration in the i-layer and the contact potential at the Sn02/P interface needs to be adjusted. Once the J- V curve had been generated, the simulation results were used to characterise the empirical cell, in both thermodynamic- and steady-state equilibrium. This simulated cell was designated the realistic cell. The effect of asymmetries in the input parameters, under carrier band mobility interchange, on the performance of p-i-n cells has been investigated. The results indicate that, while asymmetries in the gap state distributions do give rise to asymmetrical behaviour in the J- V curve, the effect is slight, and it is the positional asymmetry of the optical generation profile that is mostly responsible for the observed asymmetry in the J- V curve under mobility interchange. An investigation of the limiting carrier effect has led to the conclusion that, in a p-i-n aSi:H cell under forward bias, the electron is the limiting carrier. This has been explained by appealing to the form of the optical generation profile, since most electron-hole pairs (EHPs) are generated near the front of the cell, and it is electrons that must be collected at the back contact. Investigations of the n-i-p aSi:H cell, under forward bias, have shown the hole to be the limiting carrier. It was found that the introduction of positional symmetry into the optical generation rate profile greatly reduced the limiting carrier effect, and it was concluded that the limiting carrier effect arises due to the asymmetries in the material parameters of the cell, particularly the _ positional asymmetry of the optical generation profile. It was observed that the nature of the optical generation profile actually plays an important role in determining the identity of the limiting carrier, in a p-i-n cell. The same effect was not observed in the n-i-p cell. The effective carrier collection length has been defined, and it was seen that the limiting carrier possesses the larger effective collection length. The effect of boron and phosphorous profiling of the i-layer was studied. It was found that boron profiling led to a decrease in cell performance, while phosphorous profiling improved cell performance. It was found that there was a P concentration at which cell performance peaked. The dependence of the spectral response of the realistic cell on device length L, was investigated, showing a general improvement in the spectral response as L was decreased. The spectral response has been interpreted in a novel way. It was assumed that the form of the monochromatic optical generation profiles in the vicinity of the peak in the spectral response represented optimal generation profiles. These profiles were subjected to a linear transformation, such that their form was preserved but that their integrated value was the same as that of the realistic optical generation profile, under global AM1.5 illumination. Using these transformed optical generation profiles, J- V curves were obtained. The maximum power output PM of these J- V curves was seen to exhibit a maximum some 17% greater than that of the realistic cell with a realistic optical generation profile. The spectral response of the phosphorous profiled cell was obtained. In a manner similar to that for the non-P profiled cell, the optimal generation profile was found. The PM for this profile was found to be 7.86mWcm -2 , considerably larger than the 5.60mWcm-2 for the phosphorous profiled cell with a realistic optical generation profile. The effect on the simulation output of variations in numerous dangling-bond defect input parameters has been investigated. It was found that the energy position and concentration of the doped layer defects need not be known to a high degree of precision. On the other hand, it was found that the energy position of the i-layer defects, the standard deviation of the defect distributions, and the defect carrier capture cross-sections, do need to be known with certainty.

Diese Arbeit stellt einen Beitrag zur Modellierung der gerichteten Erstarrung von Silizium für die Photovoltaik dar. Es wurde basierend auf einem industriellen Prozesses ein Modellaufbau der Schmelze mit zwei Induktoren nach der Ähnlichkeitstheorie abgeleitet. Dieser ermöglicht, durch die Verwendung von niedrig schmelzenden Metallen, eine umfassende Messung der Strömungsgeschwindigkeiten mit Ultraschall-Velocimetrie. Basierend auf den experimen- tellen Daten wurde ein numerisches Modell zur Berechnung der Schmelzströmung unter Magnetfeldeinfluss validiert. Es wurden detaillierte Untersuchungen zu Strömungsstrukturen und beeinflussende Parameter durchgeführt, eine Methode zur Klassifizierung entwickelt und die Rotationskennzahl Ro eingeführt, mit welcher man in Abhängigkeit vom Magnetfeld und der Schmelzgeometrie die horizontale Rotation der Schmelzströmung in einem breiten Gültigkeitsbereich vorhersagen kann. Das validierte numerische Modell wurde zur Prozessoptimierung auf die Schmelzströmung des industriellen Prozesses angewendet.

Dissertação de mestrado em Engenharia Eletrónica e de Computadores
A microgeração e a utilização de veículos elétricos estão cada vez mais presentes no quotidiano e representam dois importantes fatores no caminho do desenvolvimento das smart grids e smart homes, que visam a gestão dos dispositivos eletrónicos ligados à rede elétrica ou à habitação. Assim sendo, a necessidade do desenvolvimento de novas tecnologias, assim como a otimização de topologias já existentes, no sentido de melhorar o carregamento de baterias dos veículos elétricos, a produção de energia a partir de fontes de energia renováveis e o melhoramento da qualidade da energia elétrica, é cada vez mais relevante. No âmbito desta dissertação pretende-se desenvolver um equipamento que surge como uma solução para a realização da interface entre veículos elétricos, painéis fotovoltaicos e a rede elétrica, além de compensar, dinamicamente, problemas de qualidade da energia elétrica. A solução tradicional utiliza dois conversores de potência para realizar a interface entre o veículo elétrico e a rede elétrica e mais dois conversores de potência para a interface da fonte de energia renovável e a rede elétrica). Esta topologia apresenta uma desvantagem no carregamento direto das baterias do veículo elétrico a partir da fonte de energia renovável, pois requer o uso de quatro conversores de potência e a rede elétrica como intermediários. Para colmatar esta desvantagem, a configuração adotada utiliza apenas um conversor CA-CC e um barramento CC comum aos dois conversores CC-CC que interligará os três conversores. Assim, obtêm-se as vantagens de utilizar apenas um conversor para realizar a interface do carregador do veículo elétrico e a fonte de energia renovável com a rede, a possibilidade de realizar o carregamento das baterias diretamente dos painéis fotovoltaicos, sem usar a rede como intermediário, e ainda a contribuição para a melhoria dos problemas de qualidade de energia. Nesta dissertação, foi desenvolvido um conversor CA-CC (em colaboração com outra dissertação), o mais reduzido possível (usando SiC - Silicon Carbide, como semicondutores controlados), variando assim as suas caraterísticas de forma a se obter a redução de tamanho e a realizar a interface com os outros dois conversores de potência (CC-CC). Após um estudo cuidado do estado da arte, foi desenvolvido um modelo computacional em PSIM e foi desenvolvido um protótipo laboratorial (conversor CA-CC e CC-CC), onde o conversor CC-CC realiza a interface com a fonte de energia renovável (com algoritmo de controlo de maximum power point tracker (MPPT)). Com recurso ao sistema desenvolvido foram obtidos resultados experimentais que comprovam a solução adotada.
Microgeneration and the use of electric vehicles are increasingly present in our daily lives and they represent two major factors in the development of smart grids and smart homes, which aim to manage electronic devices connected to the power grid or to the house. Therefore, the need to develop new technologies as well as improving the existing ones in order to improve battery charging of electric vehicles, the production of energy from renewable power sources and the improvement of energy quality is increasingly relevant. This dissertation intends to develop an equipment that emerges as a solution for the interface between electric vehicles, photovoltaic panels and the power grid as it also dynamically compensates for problems of power quality. The traditional solution uses two power converters to interface between the electric vehicle and the power grid (one ac/dc converter and another dc/dc converter) and two more power converters for the renewable power source (one ac/dc converter and another dc/dc converter). This traditional topology has a disadvantage in the direct charging of the electric vehicle batteries from the renewable energy source as it requires the use of four power converters and the power grid as intermediates. To overcome this drawback, the adopted configuration uses only one ac/dc converter and one common dc link to interface the two dc/dc converters with the ac/dc converter. This gives the advantages of using only one converter to interface the electric vehicle charger and the renewable power source with the power grid. It also allows the ability to charge the batteries directly from the photovoltaic panels without using the power grid as an intermediary further contributing to improve issues related to the quality of power. Through this dissertation, when combined with another dissertation, an AC/DC converter, compacted as much as possible will be developed, thus varying its characteristics in order to obtain the size reduction. This will interface with the other two power converters (dc/dc). Posteriorly and individually, a dc/dc converter will be developed that will interface with the renewable power source, where a maximum power point tracker (MPPT) control algorithm is applied in order to extract as much power as possible from the photovoltaic panel.
Este trabalho de dissertação está enquadrado no projeto de IC&DT “newERA4GRIDs – New Generation of Unified Power Conditioner with Advanced Control, Integrating Electric Mobility, Renewables, and Active Filtering Capabilities for the Power Grid Improvement”, financiado pela Fundação para a Ciência e Tecnologia, com a referência PTDC/EEI‑EEE/30283/2017.
Este trabalho de dissertação está enquadrado no projeto de IC&DT “DAIPESEV – Development of Advanced Integrated Power Electronic Systems for Electric Vehicles”, financiado pela Fundação para a Ciência e Tecnologia, com a referência PTDC/EEI EEE/30382/2017.

Σκοπός αυτής της διπλωματικής εργασίας είναι να εμβαθύνουμε στη λειτουργία φωτοβολταϊκού πλαισίου μονοκρυσταλλικού πυριτίου και μέσα από τα αριθμητικά δεδομένα των μετρήσεων και των υπολογισμών, να αποφανθούμε πώς η λειτουργία σε πραγματικές συνθήκες μπορεί να επηρεάσει την παραγόμενη ισχύ του. Στα πλαίσια αυτά, πραγματοποιήθηκαν μετρήσεις ρεύματος και τάσης, στο χώρο του τμήματος των Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών, με φωτοβολταϊκό πλαίσιο μονοκρυσταλλικού πυριτίου ισχύος αιχμής 80 W. Οι μετρήσεις γίνονταν μια φορά την εβδομάδα κατά τη διάρκεια ενός έτους περίπου (2008-2009) και στόχος ήταν να διεξαχθούν μετρήσεις υπό διάφορες συνθήκες ακτινοβολίας και θερμοκρασίας και για αρκετές γωνίες κλίσης ώστε να αποκτήσουμε μια ολοκληρωμένη εικόνα της ενεργειακής του συμπεριφοράς. Στη διάρκεια των μετρήσεων αλλάζαμε την τιμή ενός μεταβλητού φορτίου, για να πάρουμε τη χαρακτηριστική ρεύματος τάσης του συγκεκριμένου πλαισίου και επιπλέον σημειώναμε την ακτινοβολία, τη θερμοκρασία του περιβάλλοντος, του κυττάρου και της πίσω όψης του, καθώς και της κλίσης τοποθέτησης. Ακόμα ελέγχαμε πώς επηρεάζει τη χαρακτηριστική καμπύλη I-V, και κατά συνέπεια την απόδοση, τυχόν φυσική σκίαση από παρακείμενο αντικείμενο. Ο προσανατολισμός των πλαισίων ήταν πάντα προς το Νότο, ώστε να έχουμε περισσότερες ώρες ηλιοφάνειας, μίας και η Ελλάδα είναι χώρα του βόρειου ημισφαιρίου. Κατά την επεξεργασία των μετρήσεων καταλήξαμε στην βέλτιστη κλίση τοποθέτησης του πλαισίου ανά εποχή και είδαμε πως η ακτινοβολία επιδρά θετικά στην απόδοση του σε αντίθεση με τη θερμοκρασία του κυττάρου που τη μειώνει όταν αυτή αυξάνεται. Τέλος, έγινε μια σύγκριση των τιμών που δίνει ο κατασκευαστής σε εργαστηριακό περιβάλλον με τις τιμές των μετρήσεων για να διαπιστώσουμε τις απώλειες που έχουμε όταν το μονοκρυσταλλικό πλαίσιο λειτουργεί σε πραγματικές συνθήκες.
The aim of this diploma thesis is to take a better look at the operation of a monocrystalline silicon photovoltaic module and through the numerical data of measurements and the calculations, to come to a conclusion about how the operation in real conditions can influence his produced power. Measurements of current and tendency have been made in the area of the department of Electrical and Computer Engineering using a monocrystalline silicon photovoltaic module of peak power 80 W. The measurements took place once a week for about a year (2008-2009) and our goal was to obtain measurements under various conditions of radiation and temperature and for some angles of bent so that we acquire a completed picture of its energy behavior. During the measurements we changed a variable load, in order to form the characteristic curve of current and tendency of the module and we also noted down the radiation, the environmental, the cell and the back side temperature of the module, as well as the bent of placement. Moreover, we checked how a possible natural shading from an adjacent object influences the characteristic I-V curve, and as a result the efficiency of the module. The orientation of the module was always South, in order to gain more hours of sunlight, since Greece is a country of the northern hemisphere. While processing the measurements, we found the optimal bent of placement per season for the module and we saw that the radiation affects positively its efficiency contrary to the cell temperature that decreases the efficiency when increased. Finally, we compare the electrical specifications in laboratorial environment that the constructor gives, with the measurements in order to realise the losses that we have when the monocrystalline module functions in real conditions.